A known wind turbine generator in the related art generates electricity using wind power, which is natural energy. This type of wind turbine generator is configured such that a nacelle mounted on a tower is provided with a rotor head fitted with wind turbine blades, a main shaft connected to the rotor head so as to rotate together therewith, a gearbox connected to the main shaft that rotates by receiving wind power with the wind turbine blades, and a generator driven by the shaft output power of the gearbox. In the thus-configured wind turbine generator, the rotor head having the wind turbine blades that convert wind power to rotational power and the main shaft rotate to generate shaft output power, and the shaft output power, which is increased in rotational speed through the gearbox connected to the main shaft, is transmitted to the generator. Thus, power generation can be performed using the shaft output power obtained by converting wind power to rotational power as a driving source for the generator, that is, using wind power as motive power for the generator.
The conventional wind turbine generator described above is sometimes installed in a cold region in which the outside air temperature is low, at about −40° C. In such a cold region, problems such as changes in the properties of lubricant oil or low-temperature brittleness occur due to a decrease in outside air temperature; therefore, to cope with this, the devices in the nacelle are heated to a predetermined temperature using a heater or the like.
On the other hand, because the nacelle accommodates devices that generate heat during operation, such as a gearbox and a generator, a cooling structure is employed in which an air intake port and an air exhaust port are formed for preventing an increase in temperature by ventilating the nacelle interior using a fan operated by a wind turbine (for example, refer to Patent Document 1).
For wind turbine generators, a cooling mechanism has been proposed which releases heat generated from the generator to wind that has rotated a rotor, through a plurality of fins provided on a frame that partitions the outer peripheral surface of the generator and outside air from each other. This cooling mechanism does not need an air intake port, an air exhaust port, and a cooling fan (for example, refer to Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. Sho 58-65977    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2002-13467